Don't even bother calling....
One of the great shortcomings in the Do Not Call Registry is the ability of non-profit organizations making unwanted calls(thanks Congress!). With the meteoric rise in phishing attacks both online and via phone there is no way any organization that cold calls me is getting any information about me (especially my credit card!). On occasion, I have requested them to send literature to me detailing their organization, so I can consider if I want to donate to them, but not one has ever taken me up on it. I suggest you do the same, as you can never tell who is on the other side of the line. I just wish there was a way to get them to stop calling as they are just wasting their money and my time.